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Installation of modern combustion monitoring tools on engines with limited access to the combustion chamber

 

The following article focuses on the maintenance benefits of installing a cylinder pressure monitoring (CPM™) system on an unreliable and poorly running engine. AETC and Kistler were requested by the customer to inspect and resolve the ongoing problem of damage to cylinder liners, caused by combustion detonation. Over the last 10 years, the customer had lost approximately 20 cylinder liners (at an estimated cost of over $400,000) plus significant down time.

 

Modern combustion monitoring tools provide a well proven solution. Further benefits of these are increased fuel efficiency (due to less misfiring), tighter air/fuel ratio control and lower operating costs due increased confidence in unmanned operation.

 

                                                             

Situation Prior to Improvement Modifications


Engine particulars

 

Engine type is a 6 cylinder, 12 (opposed) piston Fairbanks Morse 38ETDD8 1/8, two stroke turbocharged. Dual fuel with separate PCC diesel pilot used for power generation and started using 100% diesel, then transfers to natural gas operation with diesel as pilot.



Situation Analysis

 

With the expertise in pressure sensor technology from Kistler Instruments and real time engine diagnostics from AETC a solution was proposed and accepted by the client. It was found that the cylinder liner damage was caused by detonation during engine operations at 100% load or during transfer from diesel into natural gas operation. The main part of the solution is the installation of Kistler combustion pressure sensors connected to the AETC CPM™ System for on-line data analysis. This system provides for a reliable engine shut down upon detection of detonation, cylinder balancing during 100% load operation, air / fuel ratio balancing at the cylinder level as well as shut down if other predetermined engine operating conditions are detected.

 

Additional efforts were made to improve the transition phase from diesel to natural gas operation, thus reducing the possibility of detonation.



Installation of combustion pressure sensors


The Fairbanks Morse engine does not have indicator valves to mount pressure sensors such as the proven Kistler 6613. With no other means to access the main combustion chamber the Kistler AETC team modified the existing PCC’s to accommodate the new miniature sensor type 6351 which features an M5 thread. This installation was challenging due to the size of the PCC and in particular the configuration of the water jacket. 

 











Installation of CPM™ System

 

To provide permanent monitoring of the combustion pressure signals for alarms and combustion diagnosis, AETC’s CPM™ system was installed. CPM™ was modified to provide system warnings and has the ability to shut down the engine if any critical combustion pressure parameter is reached.


The ability to shut the engine down is extremely helpful as the facility is often unmanned. The most likely occurrence of detonation was due to overload during the transfer from diesel operation into gas operation. AETC modified the main fuel manifold by adding ‘port valves’ and changed the mechanical dual fuel EGB governor to a dual governor system using the Woodward EGB and a PROACT to control the gas flow. The transfer signal from the existing controls was used by the AETC dual fuel controller to switch the fuels. Several transfer rates were tested prior to commissioning the system

 

 

Post-installation operating experience

 

The complete system was put into service on time and within budget. Since the start up half year ago, there have been no liner or sensor failures and the system has continued to work as designed. Almost immediately the site experienced the benefits of CPM™ when a pre-chamber injector failed causing the other cylinders to overload resulting in detonation. The CPM™ system shutdown the engine before any damage could occur, even before audible detection by the operators. With the additional playback feature of the CPM™ system the problem cylinder could be found and repaired without necessitating further engine diagnostics.

 

The system has enabled the operator to optimize start up, shutdown and the fuel transfer phases of engine operation whilst avoiding critical combustion conditions, such as detonation. The two main problems of engine operation (no detonation and smooth operation at 100% load) were solved. Additional benefits include improved emissions due to cylinder balancing and lower fuel consumption. Considering the ability to run and keep the engine running with no need to run the boiler the system will be paid off in a matter of months.

 

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